This disclosure generally relates to treatment of oil and gas reservoirs.
Hydrocarbons (e.g., oil, condensate and gas) may be produced from wells that are drilled into the formations containing them. For a variety of reasons, for example inherently low permeability of the reservoirs or damage to the formation caused by drilling and completion of the well, the flow of hydrocarbons into the well may be low. In this case, the well may be “stimulated” using, for example, hydraulic fracturing, matrix acidizing, or a combination thereof.
During matrix acidizing, which may also be known as acidizing, matrix acidizing, and so on under certain circumstances, acid or some other reactive chemical is pumped into the formation to react with the material (matrix) of the reservoir to increase its porosity, permeability and contact surface. Acid typically etches the formation creating a network of multiple channels contacting the wellbore. The etched channels may be known as wormholes.
During and/or in between the stages of acidizing, a product known as MAXCO3 ACID, which provides plugging and isolation of naturally occurred wormholes or small wormholes during the stimulation in order to divert a network of wormholes created during the stimulation, may be used. Plugging is achieved by pumping of a solid-laden slurry, for example containing viscoelastic diverting acid (VDA) and fibers or other solids. Information of these and other acidizing products can be found from U.S. Pat. Nos. 7,565,929, 7,380,600, 7,350,572, 7,219,731, 7,666,821, and 6,637,517, the contents of which are hereby incorporated by reference into the current disclosure in their entireties.
After the acidizing, the well is then changed into a production or injection mode. Wells that have undergone matrix acidizing in the past may include regions with large heterogeneities, and future efficient use of the well may be contingent on proper diversion, for example, by bridging or plugging the wormholes and properly addressing the heterogeneities.
Specifically, mathematical models may be built to design a treatment aimed at plugging or bridging particular regions. Known models and treatments are imperfect, however, as there has been a difficulty accurately and appropriately mapping region, especially previously stimulated regions. Specifically, models that utilize straight slot geometries to represent open channels often offer an inaccurate approximation, especially when multiple, wide heterogeneities are present in a formation or a sample thereof.